1 files changed, 178 insertions, 0 deletions
diff --git a/modules/http/prometheus.lua b/modules/http/prometheus.lua
new file mode 100644
index 0000000..3218552
--- /dev/null
+++ b/modules/http/prometheus.lua
@@ -0,0 +1,178 @@
+-- SPDX-License-Identifier: GPL-3.0-or-later
+-- Module implementation
+local M = {
+	namespace = '',
+	finalize = function (_ --[[metrics]]) end,
+}
+
+-- Gauge metrics
+local gauges = {
+	['worker.concurrent'] = true,
+	['worker.rss']        = true,
+}
+
+local function merge(t, results, prefix)
+	for _, result in pairs(results) do
+		if type(result) == 'table' then
+			for k, v in pairs(result) do
+				local val = t[prefix..k]
+				t[prefix..k] = (val or 0) + v
+			end
+		end
+	end
+end
+
+local function getstats()
+	local t = {}
+	merge(t, map 'stats.list()', '')
+	merge(t, map 'cache.stats()', 'cache.')
+	merge(t, map 'worker.stats()', 'worker.')
+	return t
+end
+
+-- @returns current stats + difference against previous data set passed in @param prev
+local function snapshot_start(prev)
+	assert(type(prev) == 'table', 'table with previous values expected')
+	local is_empty = true
+	-- Get current snapshot
+	local cur, stats_dt = getstats(), {}
+	for k,v in pairs(cur) do
+		if gauges[k] then
+			stats_dt[k] = v
+		else
+			stats_dt[k] = v - (prev[k] or 0)
+		end
+		is_empty = is_empty and stats_dt[k] == 0
+	end
+	-- Calculate upstreams and geotag them if possible
+	local upstreams
+	if http.geoip then
+		upstreams = stats.upstreams()
+		for k,v in pairs(upstreams) do
+			local gi
+			if string.find(k, '.', 1, true) then
+				gi = http.geoip:search_ipv4(k)
+			else
+				gi = http.geoip:search_ipv6(k)
+			end
+			if gi then
+				upstreams[k] = {data=v, location=gi.location, country=gi.country and gi.country.iso_code}
+			end
+		end
+	end
+	-- Aggregate per-worker metrics
+	local wdata = {}
+	for _, info in pairs(map 'worker.info()') do
+		if type(info) == 'table' then
+			wdata[tostring(info.pid)] = {
+				rss = info.rss,
+				usertime = info.usertime,
+				systime = info.systime,
+				pagefaults = info.pagefaults,
+				queries = info.queries
+			}
+		end
+	end
+	-- Publish stats updates periodically
+	if not is_empty then
+		local update = {time=os.time(), stats=stats_dt, upstreams=upstreams, workers=wdata}
+		return cur, update
+	end
+	return cur, nil
+end
+
+-- Function to sort frequency list
+local function stream_stats(_, ws)
+	local ok = true
+	-- Publish stats updates periodically
+	local prev = getstats()
+	while ok do
+		worker.sleep(1)
+		local update
+		prev, update = snapshot_start(prev)
+		local push = tojson(update)
+		ok = ws:send(push)
+	end
+end
+
+-- Transform metrics from Graphite to Prometheus format
+-- See: https://gitlab.nic.cz/knot/knot-resolver/-/issues/650
+-- E.g.:
+--  worker.ipv4 -> worker_ipv4
+--  answer.blocked;stype=A -> answer_blocked{stype="A"}
+local function get_metric(key)
+	local key_index, key_len, key_tag = 0, #key, 0
+	return select(1, key:gsub('.', function (c)
+		key_index = key_index + 1
+		if key_tag == 0 then
+			if c == '.' then return '_' end
+			if c == ';' then key_tag = 1; return '{' end
+		elseif key_tag == 1 then
+			if key_index == key_len then
+				if c == '=' then return '=""}'
+				else return c .. '"}' end
+			end
+			if c == '=' then key_tag = 2; return '="' end
+		elseif key_tag == 2 then
+			if key_index == key_len then
+				if c == ';' then return '"}'
+				else return c .. '"}' end
+			end
+			if c == ';' then key_tag = 1; return '",' end
+		end
+		return nil
+	end))
+end
+
+-- Render stats in Prometheus text format
+local function serve_prometheus()
+	-- First aggregate metrics list and print counters
+	local slist, render = getstats(), {}
+	local latency = {}
+	local counter = '# TYPE %s counter\n%s %f'
+	for k,v in pairs(slist) do
+		k = get_metric(k)
+		-- Aggregate histograms
+		local band = k:match('answer_([%d]+)ms')
+		if band then
+			table.insert(latency, {band, v})
+		elseif k == 'answer_slow' then
+			table.insert(latency, {'+Inf', v})
+		-- Counter as a fallback
+		else
+			local key = M.namespace .. k
+			local name, label = key:match('^([^{]+)(.*)$')
+			table.insert(render, string.format(counter, name, name .. label, v))
+		end
+	end
+	-- Fill in latency histogram
+	local function kweight(x) return tonumber(x) or math.huge end
+	table.sort(latency, function (a,b) return kweight(a[1]) < kweight(b[1]) end)
+	table.insert(render, string.format('# TYPE %slatency histogram', M.namespace))
+	local count, sum = 0.0, 0.0
+	for _,e in ipairs(latency) do
+		-- The information about the %Inf bin is lost, so we treat it
+		-- as a timeout (3000ms) for metrics purposes
+		count = count + e[2]
+		sum = sum + e[2] * (math.min(tonumber(e[1]), 3000.0))
+		table.insert(render, string.format('%slatency_bucket{le="%s"} %f', M.namespace, e[1], count))
+	end
+	table.insert(render, string.format('%slatency_count %f', M.namespace, count))
+	table.insert(render, string.format('%slatency_sum %f', M.namespace, sum))
+	-- Finalize metrics table before rendering
+	if type(M.finalize) == 'function' then
+		M.finalize(render)
+	end
+	return table.concat(render, '\n') .. '\n'
+end
+
+-- Export module interface
+M.endpoints = {
+	['/stats']     = {'application/json', getstats, stream_stats},
+	['/frequent']  = {'application/json', function () return stats.frequent() end},
+	['/upstreams'] = {'application/json', function () return stats.upstreams() end},
+	['/bogus']     = {'application/json', function () return bogus_log.frequent() end},
+	['/metrics']   = {'text/plain; version=0.0.4', serve_prometheus},
+}
+
+return M